Movable clipper blade and drive transmission for same



March 10, 1959 J. F. WAHL ETAL 2,876,538

MovABLE CLIPPERBLADE .AND DRIVE'LT'RANsMisswN FOR SAME Filed Oct. 8, 1956 MavfME/vr l LL.L.L.L.A.L.LL.

F I l l 3 Wardly extending axis of the end 32 makes an angle of approximately 60 degrees with the plane of spring member 22, and end plane 33 of nger member 30 is normal to this axis.

Fig. 4 is a bottom view of the forward end of finger member 30, end plane 33 of the member being in the plane of the drawing as indicated by line 4-4 in Fig. 3. The bottom corners of finger member 30 are bevelled to provide bearing surfaces. These surfaces are designated 35, 36, 37 and 3S in Fig. 4, and similarly, where appropriate, in Figs. 2, 3 and 5.

As shown in Fig. 4, each of the corner surfaces 35-38 is inclined at an angle of substantially 30 degrees to the transverse axis 39 of finger end 32. Each corner surface also is inclined at an angle of substantially degrees to the longitudinal axis of the finger end as shown in Fig. 5. Thus, each bearing surface, for example, surface 35, is inclined at substantially degrees to the transverse axis of the finger end and also inclined at an angle of substantially 20 degrees to the longitudinal axis of the finger end. The 20 degree inclination is the critical one from the standpoint of the driving relationship between the finger member and its associated blade.

The aforesaid linger member 30 of the drive transmission engages and cooperates with movable clipper blade 20 which is illustrated in Figs. 6-8 and which now will be described.

Movable blade 20 is generally rectangular in shape and it has a row of cutting teeth 40 along one of its sides.

The upper surface of blade 20 has an elongated, generally central recess 43. This recess is shaped to conform to the shape of finger end 32. Thus, the upper surface corners of recess 43 are shaped, respectively, to provide bearing surfaces 45, 46, 47 and 48. These surfaces, respectively, receive the surfaces -38 of linger end 32 and establish a wedging relationship between the finger member and the blade.

As shown in Figs. 6 and 8, each bearing surface in recess 43 has an inclination of substantially 30 degrees to the longitudinal axis of the recess (Fig. 6) and an inclination of substantially 20 degrees to a plane normal to the blade (Fig. 8).

One important structural feature of the invention is that one adjacent pair of the bearing surfaces, for ex ample surfaces 4S and 46, is spaced from the other adjacent pair, namely, surfaces 47 and 43, by an effective distance which is approximately one-half the width of blade 20 measured along the row of teeth 40. Thus, the dimension C shown in Fig. 6 must be approximately one-half the aforesaid blade width.

Another important structural feature of the invention is that dimension C must be approximately twice the length of dimension A, the latter being the distance from the forward teeth ends to the longitudinal axis of recess 43. Since dimension B (Fig. 6) is one-half dimension C, it will be seen that dimension A is approximately equal to dimension B.

In operation, blade 20 reciprocates back and forth in response to movement of finger member 30 which is carried and driven by vibrating armature 17. As previously mentioned, finger member 30 aided by spring member 22 exerts a bias or pressure on blade 20, this bias or pressure being of optimum cutting value.

Assuming blade 20 is moving to the left as viewed in Fig. 6, teeth and consequently the blade encounter a resistance indicated by R. This resistance R is applied to blade 20 on an arm indicated by dimension A. The resultant moment which is represented by the product R times A reacts on finger member 30 as a torque which under certain circumstances tends to unseat the finger member. This torque (R times A) or twisting leverage is resisted by a moment represented by the product of a force F applied by the tinger member and the arm in- Adicated by the dimension B.

When the product of F and B exceeds or equals the product of R and A, finger member 30 retains its proper seated relationship with recess 43, i. e. no unseating occurs. This is true under conditions of optimum bias.

Thus, the unseating tendency is substantially eliminated when the dimension B is greater than or at least not smaller than the dimension A, and this relationship is one of the main features of the invention. Where the dimension B is less than the dimension A it is necessary to increase the cutting bias and thus increase the value F in order to resist the tendency toward unseating and this expedient, as previously mentioned, is objectionable because it results in excess friction between blades.

Another main feature of this invention which cooperates with the dimensioning described above is the previously mentioned shape of the bearing surfaces 35-38 and 45-48. these bearing surfaces are such that close manufacturing tolerances are not required. Thus, relatively inexpensive manufacturing processes may be followed in shaping the surfaces 35--38 on the finger and the surfaces 45-48 in blade 20. Minor deviation from the desired shapes in manufacture do not result in failure of bearing engagement as would be the case, for example, if an inclination of substantially less than 20 degrees were used in place of the substantially 20 degrees specified.

To summarize, it has been found that the substantially 2O degree angle is as steep as practical for simplified, inexpensive manufacturing processes. Further, the bias pressure between blades is restricted to that necessary only for proper cutting action. Elimination of the unseating tendency under conditions of optimum bias pressure and extreme loads is accomplished by increasing the width of the finger member to a dimension which is approximately one-half the width of the blade or which is approximately twice the distance between the longitudinal axis of the recess and the forward end of the cutting teeth. The leverage provided by the respective bearing surfaces thus is increased without increasing the bias pressure, and the transmission is such that unseating ordinarily does not occur even at loads high enough to stall the motor, i. e., loads which impose maximum torque or twisting leverage on finger member 30.

From the above description it is thought that the construction and advantages of our invention will be readily apparent to those skilled in the art. Various changes in detail may be made without departing from the spirit or losing the advantages of the invention.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

A movable clipper blade and drive transmission for same comprising a blade having a row of teeth along one longitudinal edge and having a central elongated recess extending widthwise in the upper surface thereof, the extremities of said recess each having a pair of double-inclined bearing surfaces, each bearing surface inclined at an angle of about 30 degrees with the longitudinal axis of the recess and at an angle of about 20 degrees with a plane normal to the blade, the said pairs of bearing surfaces spaced from each other by approximately twice the distance from said teeth to the longitudinal axis of said recess, said spacing corresponding approximately to one-half the width of the blade, a drive finger having bearing surfaces disposed and shaped to be seated on the bearing surfaces of said recess, and vibrating means secured to said drive finger and biasing same against said blade with optimum cutting pressure.

References Cited in the file of this patent UNITED STATES PATENTS 431,965 Cook et al. July 8, 1890 1,708,315 Lutes Apr. 9, 1929 2,306,039 Cromonic Dec. 22, 1942 2,640,261 Wahl June 2, Y19,53

The described shape or inclinations of 

